#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
    int a1 = 1;
    int n;
    int a0 = 1;
    scanf_s("%d", &n);
    int res = 0;
    for (int i = 1; i < n - 1; i++)
    {
        res = a0 + a1;
        a0 = a1;
        a1 = res;
    }
    printf("%d", res);
    return 0;
}